Working with Arrays and Collections →hardMultiple ChoiceObjective-mapped

1Z0-829 Working with Arrays and Collections Practice Question

Which statement about TreeSet is true when using a custom Comparator that does not define equals() consistently with compare()?

⚠ Common exam trap

Watch out — candidates often assume TreeSet uses equals() for duplicate detection because of the general Set contract, but TreeSet (and TreeMap) specifically override that behavior to use compare()/compareTo() instead.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

TreeSet considers two elements equal if the comparator returns 0.

TreeSet uses the compare() method of the provided Comparator (or the natural ordering's compareTo()) to determine element equality. When a custom Comparator returns 0 for two elements, TreeSet treats them as duplicates and does not add the second element, regardless of what equals() returns. This is specified in the Java Collections Framework documentation and is critical for maintaining the Set contract.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
TreeSet uses equals() to determine duplicates.
Why it's wrong here
Uses compare/compareTo.
✗
TreeSet uses hashCode() for ordering.
Why it's wrong here
Ordering is based on compare/compareTo.
✓
TreeSet considers two elements equal if the comparator returns 0.
Why this is correct
Set uses comparator's compare method.
✗
TreeSet throws IllegalArgumentException if equals() is inconsistent.
Why it's wrong here
No exception; but behavior may violate Set contract.

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1Z0-829 Working with Arrays and Collections Practice Question

Why each option matters

Option-by-option breakdown

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